Design and Cold Testing of a Bi-Periodic Angular Radial RF Circuit for a C-Band Extended Interaction Oscillator

A C-band angular bi-periodic angular radial EIO (BPAREIO) is proposed for high-power microwave (HPM) applications. It offers miniaturization, high efficiency, and low magnetic field operation. A divergent angular radial sheet electron beam (ARSEB) with an angle of 14° and a current of 101 A is employed to operate the seven-gap angular radial cavities. Angular radial cavities are coupled by two sectoral cavities having an opening angle $\beta $ . Cavity characteristics, such as dispersion, scattering parameters, normalized beam conductance, electric field distribution, and stability, are analyzed to optimize the design for $\pi $ -mode operation. To further enhance the performance of BPAREIO, ridges are incorporated into interaction gaps near the beam tunnel. This modification leads to an enhanced radial electric field near the beam tunnel, increasing characteristic impedance (R/Q). In particle-in cell (PIC) simulations, ridge-loaded BPAREIO demonstrated in modeling an RF peak output power of 6.2 MW at a frequency of 5.805 GHz when applying a beam voltage of 89 kV and a magnetic field of 0.3 T, yielding a peak power efficiency of 69.5%. In contrast, the BPAREIO without ridges expected a peak output power of 5.4 MW and an efficiency of 59.5% at 5.885 GHz, using the same beam parameters. Consequently, the ridge-loaded BPAREIO predicted a 16.7% increase in peak electronic efficiency compared with the BPAREIO without ridges. Moreover, ridge-loaded BPAREIO is fabricated, and experimental results closely match those obtained from simulation.